This invention relates to electronics assemblies, for example to computer systems, and to thermal management thereof.
Certain systems may be employed as servers, for example in local area networks (LANs), or in wide area networks (WANS), telecommunications systems or other operations such as database management or as internet servers. Such servers may be used in so-called “horizontally scaled” applications in which tens or hundreds of corresponding servers are employed as part of a distributed system.
A typical computer employed for such purposes will comprise a pair of microprocessors mounted on a circuit board, together with other components such as power supply units (PSUs), hard disc drives (HDDs), fans, digital video disc (DVD) players, memory modules, ethernet ports etc. The servers may be designed in modular form so that they can be stacked together with other corresponding servers in large racks. For example, some servers may be designed with a height in the order of 10 cm and a width in the order of 5 cm.
Whatever the dimensions of the assembly, it can often be a problem to ensure that such systems are cooled adequately in view of the relatively large number of electronics components in an enclosed environment. The assembly enclosure may be provided with one or more enclosure fans in one of the assembly walls which provide a flow of air through the assembly, e.g. from front to back.
However, as microprocessors have become more powerful, they therefore generate larger quantities of heat, 20 to 30 watts of heat output or higher not being uncommon. It has accordingly been difficult to ensure adequate cooling of the microprocessors. In addition, the servers may not always be employed in data centres with air conditioned environments, and ambient temperatures may therefore be relatively high. For example, the NEBS standard requires that such a system will operate at ambient temperatures of up to about 55° C. without the junction temperature of the components exceeding their specification, for example about 85° C.
Furthermore, because of relatively restricted lateral dimensions of the enclosures, it is often the case that one of the microprocessors is placed in front of the other, with the result that the rearmost processor receives cooling air that has already been heated by the front processor.